Safety trip controls provide a quick means for deactivating the machine in
an emergency situation.

A pressure-sensitive body bar, when depressed, will deactivate the
machine. If the operator or anyone trips, loses balance, or is drawn
toward the machine, applying pressure to the bar will stop the operation.
The positioning of the bar, therefore, is critical. It must stop the
machine before a part of the employee's body reaches the danger area.
Figure 40 shows a pressure-sensitive body bar located on the front of a
rubber mill.

When pressed by hand, the safety deactivates the machine. Because the
triprod has to be actuated by the operator during an emergency situation,
its proper position is also critical. Figure 41 shows a triprod located
above the rubber mill. Figure 42 shows another application of a triprod.

Safety tripwire cables are located around the perimeter of or near the
danger area. The operator must be able to reach the cable with either
hand to stop the machine. Figure 43 shows a calender equipped with this
type of control, while Figure 44 shows a tomato sorter with a safety
tripwire cable.

All of these tripwire rods or other safety devices must be manually reset
to restart the machine. Simply releasing the tripwire to restart the
machine will not ensure that the employee is out of danger when the
machine restarts.

Two-Hand Control

The two-hand control requires constant, concurrent pressure by the
operator to activate the machine. This kind of control requires a
part-revolution clutch, brake, and a brake monitor if used on a power
press as shown in Figure 45. With this type of device, the operator's
hands are required to be at a safe location (on control buttons) and at a
safe distance from the danger area while the machine completes its closing
cycle.

When the light field is broken by any part of the operator's body during the cycling

process, immediate machine braking is activated

Can allow freer movement for operator.

Simplicity of use

Used by multiple operators

Provide passerby protection

No adjustment required

Does not protect against mechanical failure

Limited to machines that can be stopped

Radiofrequency (optical)

Machine cycling will not start when the capacitance field is interrupted

When the capacitance field is disturbed by any part of the operator's body during the cycling process,

immediate machine braking is activated

Can allow freer movement for operator.

Does not protect against mechanical failure

Antennae sensitivity must be properly adjusted; this adjustment must be maintained properly

Limited to machines that can be stopped

Electromechanical

Contact bar or probe travels a predetermined distance between the operator and the danger area.

Interruption of this movement prevents the starting of machine cycle.

Can allow access at the point of operation

Contact bar or probe must be properly adjusted for each
application; this adjustment must be maintained properly

Pullback

As the machine begins to cycle, the operator's hands are pulled out of the danger area

Eliminates the need for auxiliary barriers or other interference at the danger area

Limits movement of operator May obstruct work space around operator

Restraint (holdback)

Prevents the operator from reaching into the danger area

Little risk of mechanical failure

Adjustments must be made for specific operations and for each individual

Requires frequent inspections and regular maintenance

Requires close supervision of the operators's use of the equipment

Limits movement of operator

May obstruct work space

Adjustments must be made for specific operations and each individual

Safety trip controls:

Pressure-sensitive body bar

Safety triprod

Safety tripwire

Stops machine when tripped

Simplicity of use

All controls must be manually activated

May be difficult to activate controls because of their location

Only protects the operator

May require special fixtures to hold work

May require a machine brake

Two-hand control

Concurrent use of both hands is required, preventing the operator from entering the danger area

Operator's hands are at a pre- determined location

Operator's hands are free to pick up a new part after first half of cycle is completed

Requires a partial cycle machine with a brake

Some two-handed controls can be rendered unsafe by holding with arm or blocking, thereby
permitting one-hand operation

Protects only the operator

Two-hand trip

Concurrent use of two hands on separate controls prevents hands from being in danger area when
machine cycle starts

Operator's hands are away from danger area

Can be adapted to multiple operations

No obstruction to hand feeding

Does not require adjustment for each operation

Operator may try to reach into danger area after tripping machine

Some trips can be rendered unsafe by holding with arm or blocking, thereby permitting one-hand operation

Protects only the operator

May require special fixtures

Gate

Provides a barrier between danger area and operator or other personnel

Can prevent reaching into or walking into the danger area

May require frequent inspection and regular maintenance

May interfere with operator's ability to see the work

Two-Hand Trip

The two-hand trip in Figure 46 requires concurrent application of both the
operator's control buttons to activate the machine cycle, after which the
hands are free. This device is usually used with machines equipped with
full-revolution clutches. The trips must be placed far enough from the
point of operation to make it impossible for the operator to move his or
her hands from the trip buttons or handles into the point of operation
before the first half of the cycle is completed. The distance from the
trip button depends upon the speed of the cycle and the band speed
constant. Thus the operator's hands are kept far enough away to prevent
them from being placed in the danger area prior to the slide/ram or blade
reaching the full "down" position.

To be effective, both two-hand controls and trips must be located so that
the operator cannot use two hands or one hand and another part of his/her
body to trip the machine.

A gate is a movable barrier that protects the operator at the point of
operation before the machine cycle can be started. Gates are, in many
instances, designed to be operated with each machine cycle.

Figure 47 shows a horizontal injection molding machine with a gate. To
be effective, the gate must be interlocked so that the machine will not
begin a cycle unless the gate guard is in place. It must be in the closed
position before the machine can function.

Another potential application of this type of guard is where the gate is a
component of a perimeter safeguarding system. Here the gate may provide
protection not only to the operator but to pedestrian traffic as well.

Safeguarding by Location/Distance

The examples mentioned below are a few of the numerous applications of the
principle of safeguarding by location/distance. A thorough hazard
analysis of each machine and particular situation is absolutely essential
before attempting this safeguarding technique.

To consider a part of a machine to be safeguarded by location, the
dangerous moving part of a machine must be so positioned that those areas
are not accessible or do not present a hazard to a worker during the
normal operation of the machine. This may be accomplished by locating a
machine so that the hazardous parts of the machine are located away from
operator work stations or other areas where employees walk or work. This
can be accomplished by positioning a machine with its power transmission
apparatus against a wall and leaving all routine operations conducted on
the other side of the machine. Additionally, enclosure walls or fences
can restrict access to machines. Another possible solution is to have
dangerous parts located high enough to be out of the normal reach of any
worker.

The feeding process can be safeguarded by location if a safe distance can
be maintained to protect the worker's hands. The dimensions of the stock
being worked on may provide adequate safety.

For instance, if the stock is several feet long and only one end of the
stock is being worked on, the operator may be able to hold the opposite
end while the work is being performed. An example would be a single-end
punching machine. However, depending upon the machine, protection might
still be required for another personnel.

The positioning of the operator's control station provides another
potential approach to safeguarding by location. Operator controls may be
located at a safe distance from the machine if there is no reason for the
operator to tend it.

Feeding the Ejection Methods to Improve Operator Safety

Many feeding and ejection methods do not require the operator to place his
or her hands in the danger area. In some cases, no operator involvement is
necessary after the machine is set up. In other situations, operators can
manually feed the stock with the assistance of a feeding mechanism.
Properly designed ejection methods do not require any operator involvement
after the machine starts to function.

Some feeding and ejection methods may even create hazards themselves. For
instance, a robot may eliminate the need for an operator to be near the
machine but may create a new hazard itself by the movement of its arm.

Using these feeding and ejection methods does not eliminate the need for
guards and devices. Guards and devices must be used wherever they are
necessary and possible in order to provide protection from exposure to
hazards.

Types of feeding and ejection methods...

Automatic feeds reduce the exposure of the operator during the work
process, and sometimes do not require any effort by the operator after the
machine is set up and running.

In Figure 49, the power press has an automatic feeding mechanism. Notice
the transparent fixed enclosure guard at the danger area.

With semiautomatic feeding, as in the case of a power press, the operator
uses a mechanism to place the piece being processed under the ram at each
stroke. The operator does not need to reach into the danger area, and the
danger area is completely enclosed.

Figure 51 shows a chute feed. It may be either a horizontal or an
inclined chute into which each piece is placed by hand. Using a chute
feed on an inclined press not only helps center the piece as it slides
into the die, but may also simplify the problem of ejection.

A plunger feed is shown in Figure 52. The blanks or pieces are placed in
the nest one at a time by the plunger with pushes them under the slide.
Plunger feeds are useful for operations on irregularly shaped workpieces
which will not stack in a magazine or will not slide easily down a gravity
chute. The mechanism shown is mechanically connected to the press
tripping mechanism. When the plunger is pushed in, pin "B" is allowed to
rise up into hole "A," allowing yoke "C" to release so the press can be
tripped.

The sliding die in Figure 54 is pulled toward the operator for safe
feeding and then pushed into position under the slide prior to the
downward stroke. The die moves in and out by hand or by a foot lever.
The die should be interlocked with the press to prevent tripping when the
die is out of alignment with the slide. Providing "stops" will prevent
the die from being inadvertently pulled out of the slides.

Figure 55 shows a sliding bolster. The press bed is modified with a
hydraulically or pneumatically controlled bolster that slides in when
"start" buttons are depressed, and out when the stroke is completed.

Figure 56 shows a double-dial feed. The dials revolve with each stroke of
the press. The operator places the part to be processed in a nest on the
dial which is positioned in front of the die. The dial is indexed with
each upstroke of the press to deliver the nested part into the die.

Automatic ejection may employ either an air-pressure or a mechanical
apparatus to remove the completed part from a press. It may be
interlocked with the operating controls to prevent operation until part
ejection is completed. This method requires additional safeguards for
full protection of the operator.

As shown in Figure 57, the pan shuttle mechanism moves under the finished
part as the slide moves toward the "up" position. The shuttle then
catches the part stripped from the slide by the knockout pins and deflects
it into a chute. When the ram moves down toward the next blank, the pan
shuttle moves away from the die area.

Figure 60 shows a semiautomatic ejection mechanism used on a power press.
When the plunger is withdrawn from the die area, the ejector leg, which is
mechanically coupled to the plunger, kicks the completed work out.

Essentially, robots perform work that would otherwise have to be done by
an operator. They are best used in high-production processes requiring
repeated routines where they prevent other hazards to employees. However,
they may create hazards themselves, and if they do, appropriate guards
must be used.

Figures 61, 62, and 63, respectively, show a type of robot in operation,
the danger areas it can create, and an example of the kind of task
(feeding a press) it can perform.

Work pieces are ejected by mechanical means which are initiated by the operator

Operator does not have to enter danger area to remove finished work

Other guards are required for operator protection

May not be adaptable to stock variation

Robots

They perform work usually done by operator

Operator does not have to enter danger area

Are suitable for operations where high stress factors are present, such as heat and noise

Can create hazards themselves

Require maximum maintenance

Are suitable only to specific operations

Miscellaneous Aids

While these aids do not give complete protection from machine hazards,
they may provide the operator with an extra margin of safety. Sound
judgment is needed in their application and usage. Below are several
examples of possible applications.

An awareness barrier does not provide physical protection, but serves only
to remind a person that he or she is approaching the danger area.
Generally, awareness barriers are not considered adequate when continual
exposure to the hazard exists.

Figure 64 shows a rope used as an awareness barrier on the rear of a power
squaring shear. Although the barrier does not physically prevent a person
from entering the danger area, it calls attention to it. For an employee
to enter the danger area, it calls attention to it. For an employee to
enter the danger area, an overt act must take place, that is, the employee
must either reach or step over, under or through the barrier.

Special hand tools may be used to place or remove stock, particularly from
or into the point of operation of a machine. A typical use would be for
reaching into the danger area of a press or press brake. Figure 67 shows
an assortment of tools for this purpose. Holding tools should not be used
instead of other machine safeguards; they are merely a supplement to the
protection that other guards provide.

A push stick or block, such as those in Figure 68, may be used when
feeding stock into a saw blade. When it becomes necessary for hands to be
in close proximity to the blade, the push stick or block may provide a few
inches of safety and prevent a severe injury. In the illustration the
push block fits over the fence.